when mashing in my oven should i have the temperature the same as the mash or should i have it lower, i imagine if i had it the same as the mash it might actually heat the mash up some? im mashing my beer at 150 F should i have my oven at this temp or lower?

You may want to try it a hair lower around 125, and then see how it is after 30 min or so as a test. Do you have a digital thermometer with a cord, that you can keep outside your stove and watch the temp?

I used to mash in the oven. If I set it to 175F it would maintain temp. At 200F I could mash out in about two hours. This was with two 12qt pots.

Just as you say, try it and see. You have a big pot and any temperature change will take place slowly. Keep your eye on it and you’ll be fine. Bear in mind that your oven will be off with you opening it every ten minutes.

when mashing in my oven should i have the temperature the same as the mash or should i have it lower, i imagine if i had it the same as the mash it might actually heat the mash up some? im mashing my beer at 150 F should i have my oven at this temp or lower?

Well, no...if the outside temp is 150° (which also happens to be your target mash temp) then the mash temp isn't going to rise. The mashing process isn't an exothermic reaction.

I mash in my oven. I've found that if I have it on during the mash it gets warmer at the bottom of my pot than at the top. What I do is preheat the oven, heat my strike water on the stove, take it off the heat and add my grains (I like to over shoot my temperature slightly and then stir until it gets down to the right temp). Then once my mash is at the right temperature I turn the oven off and stick it in. The pot maintains it temperature pretty well by itself anyway so the oven only has to be warm enough to help insulate the pot from the room temperature air so it cools down more slowly.

Yes you should always preheat the oven. In fact, you should always preheat your oven about 25 degrees hotter than you want it. You can easily lose 25 degrees in the oven just by opening the door. So set your oven at 150 or so and pre heat it. When ready open the door, put your pot in, close the door, turn the oven off.